Light emitting diodes (LEDs) are increasingly utilized for illumination and display applications since high power LEDs are available at low costs. In order to provide a constant light intensity light emitting diodes have to be driven with a constant load current.
For driving a single LED or a plurality of LEDs with a constant current special driver circuits have been developed. When driving a very large number of LEDs, such as LED matrices employed in LED display devices efficiency becomes a major issue as well as a precise load current setting in order to ensure a homogeneous emission of light throughout the matrix. Connecting several LEDs in series may reduce the power dissipation in the driver circuits. However, the brightness of the LEDs cannot be individually controlled which is particularly desirable when using LEDs of different colors for additive mixing of colors.
The use of switched mode power supplies for driving a number of LEDs is known per se. However, known approaches may not enable a brightness control for each individual LED, undesired current mismatch between LEDs may occur due to tolerances, and often a number of bulky inductors may be required.
There is a need for a novel low power loss LED driver circuit that enables the individual brightness control of the connected LEDs. Further, a fault detection may be desirable to identify and, optionally, bypass defective LEDs.